Modern inventory systems, such as those in mail order warehouses, supply chain distribution centers, airport luggage systems, and custom-order manufacturing facilities, face significant challenges in responding to requests for inventory items. As inventory systems grow, the challenges of simultaneously completing a large number of packing, storing, and other inventory-related tasks become non-trivial. In inventory systems tasked with responding to large numbers of diverse inventory requests, inefficient utilization of system resources, including space, equipment, and manpower, can result in lower throughput, unacceptably long response times, an ever-increasing backlog of unfinished tasks, and, in general, poor system performance.
Expanding the size or capabilities of many inventory systems requires significant changes to existing infrastructure and equipment. As a result, efforts are made to increase the utilization of space bounded by a finite infrastructure by increasing the density of packing in both horizontal and vertical directions. For example, inventory systems are now occasionally split between ground floors and mezzanine levels within a large structure. However, moving inventory items into or out of densely packed storage areas or multilevel storage areas can be inefficient using existing ground-based units or conventional vertical displacement mechanisms like elevators.